Acute Aortocaval Fistula Secondary to Chronic Type 1 B Abdominal Aortic Aneurysm Endoleak

Abstract

Aortocaval fistula (ACF) is a rare complication of abdominal aortic aneurysms (AAA), involving less than 1% of all AAA and is associated with high morbidity and mortality; it is even more uncommon, following endovascular aneurysm repair. The clinical presentation can be variable and making the diagnosis can be difficult. It can present with symptoms and signs of an abdominal emergency or systemic hypoperfusion. The traditional method of repair has been open surgery, which is associated with a high mortality rate. Endovascular repair has become more common, but results are difficult to interpret due to the low incidence of ACF. A high index of suspicion is imperative to avoid delay in diagnosis and care.

A 61-year-old male presented to his local emergency department with complaints of worsening dyspnea at rest, not associated with coughing, for several weeks. His past medical history was significant for coronary artery disease with previous cardiac catheterization and stent placement, congestive heart failure, active chronic lymphocytic leukemia (CLL), and an 8.5 × 8.3 cm AAA, which was repaired with a bifurcated endograft, 6 years earlier. He has been on multiple chemotherapy regimens to treat CLL with only brief periods of remission. Recently; however, he was failing to respond to therapy.

Admission physical exam was notable for prominent jugular venous distention and bilateral lower extremity edema, but was otherwise normal. Peripheral vascular examination was normal. Noncontrast computed tomography (CT) of the abdomen/pelvis was obtained to evaluate for CLL progression with Richter's transformation, which demonstrated no significant adenopathy, but an incidental “dislodged endograft.”

Preliminary assessment of the radiographs showed an 8.5 × 8.3 cm AAA sac with a bifurcated endograft in place ( Fig. 1 ). The proximal portion of the graft was well apposed; however, there was a type 1 B endoleak with the right limb of the graft dislodged and lying in the proximal aneurysm sac; there was a 7.5 cm aorto/right iliac artery aneurysm. Review of surveillance imaging from the previous 2 years revealed that the type 1 B endoleak was present for just over 18 months; the right iliac artery aneurysm measured 7.1 cm. It was unclear, what the surveillance frequency was for his previous endograft repair, and what the initial size of the aneurysm was. Repair was recommended; however, the patient continued to decline clinically from his other comorbidities.

Fig. 1.

Computed tomography (CT) angiogram showing abdominal aortic aneurysms (AAA) after endograft repair with dislodged right iliac limb of the bifurcated graft floating in the aneurysm in axial (A) and sagittal (B) section (white arrow).

Several days later, he became acutely hypotensive with rapid progression to pulseless electrical activity (PEA) arrest. Emergent CT angiogram ( Fig. 2 ) demonstrated an increase in size of the aorto/right iliac artery aneurysm to 9.6 × 8 cm and a large, acute aortocaval fistula. The patient rapidly progressed to worsening right heart failure, requiring high doses of vasopressor support, and the family requested comfort measures.

Fig. 2.

Computed tomography (CT) angiogram showing aortocaval fistula in axial (A) and coronal (B) section. Note the simultaneous contrast filling of both the abdominal aortic aneurysms (AAA) and the inferior vena cava (white arrow).

Discussion

Aortocaval fistula is a rare complication of abdominal aortic aneurysms and involves less than 1% of all AAA; this number increases from 2 to 6.7% in the case of ruptured AAA. ^{1 2} Graft migration is believed to be the inciting factor in cases of aortocaval fistula (ACF) after endovascular aneurysm repair (EVAR). Diagnosing ACF requires a high degree of clinical suspicion and appropriate radiographic imaging. The most common presenting symptom is low back pain, while common clinical findings include a continuous abdominal bruit, and a pulsatile abdominal mass. ^{3 4 5} Other clinical signs include high-output cardiac failure, acute lower limb ischemia, cyanosis, and increased central venous pressure (CVP). CT angiography is the primary imaging modality although, color-flow Doppler's ultrasonography and magnetic resonance angiography are utilized. ^{1 2 3} More invasive methods include arteriography, as well as venography with balloon-tipped catheters to evaluate pressure gradients and changes in oxygen saturation. ^{1 2 3 4 5 6 7 8}

Operative management has traditionally been open by surgical repair, where the fistula is then closed primarily or patched, followed by repair of the aortic aneurysm. Evacuation of the aneurysm thrombus must be done carefully to avoid pulmonary embolism. In difficult cases, ligation of the inferior vena cava (IVC) or even the aorta (with concomitant anatomic or extra-anatomic bypass) may be necessary. One of the largest modern case series (14 patients) reported a mortality rate of 7.1% for open operative repair. ² In the 1991, Brewster and colleagues published a 30-year-review of operative management for aortocaval and other arteriovenous fistulas reporting a 10% mortality rate (2/20). ⁴ A larger review based on combined published data by Calligaro et al demonstrated a 28% 30-day-mortality rate. ⁵ It is likely that institutional volume and surgeon experience coupled with the advent of better monitoring, surgical and anesthetic techniques, may have a more positive impact on outcomes.

Endovascular repair of ACF has increased in frequency, since it was first described in the 1998. ^{3 6} Endovascular stent grafting is appealing because of reduced blood loss, use of local anesthesia versus general anesthesia, shorter length of stay, and reported lower rates of postoperative complications. ^{1 3} Due to the low rate of occurrence of ACF, there is a lack of large prospective studies that evaluate the long-term outcomes of endovascular repair. Most published reports are individual cases or small case series and though, most of these suggest excellent results with few reports of poor outcomes, one should be aware of publication bias due to unwillingness to publish poor outcomes coupled with the low incidence of ACF. ^{1 3} One small case series by Akwei reported a 75% mortality in patients, who underwent endovascular management of ACF. ³ All the patients in that series, who died, had significant delays in diagnosis and time to intervention. There are no specific protocols for the endovascular management of ACF; however, some advocate following algorithms for ruptured AAA. ¹ Strategies described include endograft placement in the aorta with exclusion of the fistula, or hybrid procedures that entail stenting of the IVC to exclude the fistula, followed by operative repair of the aneurysm along with closure of the fistula. ^{3 4 5 6 7 8} The most common procedure related complication after endovascular repair was a type II endoleak; other less common complications include graft thrombosis, stenosis, prolapse into the IVC, and even IVC thrombosis. ^{9 10}

Conclusion

ACF formation after endograft repair is a rare entity that can have significant morbidity and mortality. Detection requires a high degree of suspicion and confirmatory testing, while a delay in diagnosis may lead to increased morbidity even if proper treatment is eventually undertaken by experienced specialists. Although, open repair is associated with rapid hemodynamic changes, endovascular interventions, are gaining in popularity although, long term data on durability are lacking.